PROJECT SUMMARY Cerebral palsy is the most common pediatric movement disorder and is caused by damage to brain areas during development. Children with unilateral cerebral palsy (UCP), the most common form of cerebral palsy, have unilateral impairments that cause muscle weakness, poor coordination, and difficulty grasping objects. These upper-extremity (UE) impairments reduce children's ability to participate in age-appropriate activities. There is an urgent need for effective hand therapies based on mechanisms of motor recovery. Growing evidence indicates that skill-based training affords the opportunity to capitalize on residual brain plasticity in children with UCP and improve hand function. Yet, the diversity of brain injuries, and subsequent brain reorganization in children with UCP, leads to heterogeneous outcomes even for the most established therapies. Our long-term goal is to optimize the effectiveness of therapies by adapting them to the individual characteristics of children with UCP. A critical precursor to this goal is characterizing how motor pathways adapt following perinatal brain injury. However, how best to examine brain networks underlying control of the affected UE remains unknown. The objective of this project to use a multimodal approach to identify atypical functional and anatomical patterns of connectivity in children with UCP and relate these patterns to impairment in unimanual and bimanual function. Characterizing mechanisms of motor pathway reorganization will serve as a critical precursor to the development of individualized rehabilitation approaches. We propose to use measurements of functional cortical activity (i.e. functional near-infrared spectroscopy) and transcranial magnetic stimulation to determine the unique brain areas responsible for control of the affected upper-extremity in children with UCP. We will examine these patterns in relation to standardized assessments of dexterity and performance of bimanual skills. We will leverage the information gained from this study to generate new hypotheses about potential neural targets for functional recovery. Thus, our work will inform the design of a future large-scale trial testing neurorehabilitation strategies based on individual motor pathway reorganization.